1. Field of the Invention
The present invention relates to a locking system for mobile, offshore self elevating "jack-up units" or "jack-up rigs" that are commonly used in the offshore oil industry. More particularly the present invention relates to an improved system for locking the legs and barge of a jack-up rig once the legs are in a lowered, and the hull is elevated to an operating position, (also afloat when the hull is being towed) wherein a pair of opposed actuators thrust a movable toothed chock member that fits a similar, corresponding set of teeth on the jack-up rig leg. After the pair of opposed movable toothed chock members are in place then the upper and lower wedge shaped locking members that cooperates with a pair of fixed, rigid wedged shaped locking members that are a part of the barge structure are individually moved into a locked position with the toothed chock members.
2. General Background
A "jack-up unit" or "jack-up platform" refers to any type of floating barge having a deck working platform and extendable legs used to engage the seabed and to elevate the barge or hull above the seabed. Jack-up units are used for the drilling of oil and gas wells, the production of oil and gas from wells, and related other tasks such as for example work over, maintenance, surveys and the like.
Jack-up rigs typically use three or four movable legs, each independently movable with respect to a barge or hull portion that floats. The plurality of legs can be lowered to engage the ocean floor. Jacking mechanisms then elevate the barge above the water surface. During this operation, the bottom of the legs engage the sea bottom for support, Jack-up rigs can thus relocate from one site to another site by simply elevating the legs once a job is completed, lowering the barge to the water's surface. The barge then floats with the legs extended above the barge deck. The floating barge can then be moved to a new job site and raised to an elevated position for its next duty.
An example of a jack-up platform can be seen in U.S. Pat. No. 4,657,437 issued to applicant herein, John O. Breeden and entitled "Mobile Offshore Self-Elevating Jackup Support System with Adjustable Leg Inclination and Fixation". U.S. Pat. No. 4,657,437 is hereby incorporated herein by reference.
Most commercially available jack-up rigs employ a pinion drive jacking system. This jacking system includes a plurality of rotary pinion gears that are powered. Each of the pinion gears engages a toothed rack that extends linearly along a jack-up rig leg. There may be multiple rows of teeth on each leg, and multiple pinion gears for engaging these toothed rack sections.
Jack-up units have been equipped with rack and pinion type jacking systems for many years. Examples, include U.S. Pat. No. 2,308,743 issued Jan. 19, 1943 to W. Bulkey et al.; U.S. Pat. No. 3,183,676 issued May 18, 1965 to R. LeTourneau; U.S. Pat. No. 3,606,251 issued Sep. 20, 1971 and Reissue patent U.S. Pat. No. RE29,539, owned by Armco Steel Corporation, and U.S. Pat. No. 4,813,814 entitled "Leg Holding Device for Offshore Platform".
Many other patents further illustrate the art relating to jack-up units and related structures. U.S. Pat. No. 4,813,814 provides a leg-holding device for offshore platform. U.S. Pat. No. 4,744,698 provides a method and apparatus for installing marine silos. U.S. Pat. No. 4,740,108 discloses a method and apparatus for selecting and maintaining the level of a pier deck. U.S. Pat. No. 4,668,127 provides a mobile, offshore, jack-up marine platform adjustable for sloping sea floor. U.S. Pat. No. 4,662,787 discloses a locking device for locking offshore work platform to leg chord used for lifting work platform. U.S. Pat. No. 4,657,438 provides an advancing mechanism and system utilizing same for raising and lowering a work platform.
U.S. Pat. No. 4,655,640 provides an advancing mechanism and system utilizing same for raising and lowering a work platform U.S. Pat. No. 4,627,768 relates to a locking device for oil platforms. U.S. Pat. No. 4,589,799 relates to a device for locking platform of an offshore structure. U.S. Pat. No. 4,583,881 provides a mobile offshore jack-up marine platform adjustable for a sloping sea floor. U.S. Pat. No. 4,574,650 relates to a force limiting gear reducer for the lifting pinion of a self-elevating platform. U.S. Pat. No. 4,538,938 provides an adjustable locking chock system. U.S. Pat. No. 4,521,134 provides an elevating device for an artificial island or work platform. U.S. Pat. No. 4,505,616 provides a self-locking chock system for a jack-up rig unit.
U.S. Pat. No. 4,497,591 provides an advancing mechanism and system utilizing same for raising and lowering a work platform.
One of the problems encountered by locking systems for jack-up rigs is the problem of severe loads that are encountered in rough weather conditions. Rough weather conditions create "storm loads" on leg racks that often exceed the rating or holding capacity of the elevating jacks. In these conditions, the loads must be transferred directly between the hull or barge structure and the legs with a separate locking system. These high stresses often take the form of extreme bending moments that can freeze the locking mechanism to a degree that leg movement is thereafter difficult or impossible. The present locking systems are not suitable and/or made for automatic operations and require many man-hours to install or remove. Existing locking system suffer in that they require visual identification that the locking elements are aligned before locking can occur.